oxygen-atoms of the water, is transferred from the copper towards the zinc side.

m. Similar actions take place when zinc and copper are immersed in other liquids. From nitric acid zinc takes oxygen, while negative electricity passes over to the liberated nitric oxide gas. From sulphuret of potassium, containing several atoms of sulphur, zinc takes sulphur,—and negative electricity passes over to the sulphuret of potassium, which has thus been deprived of part of its sulphur: and so on.

n. The rest of the metals and other perfect conductors exhibit relations similar to those of zinc and copper, at least when one of the two conducting bodies immersed in a liquid is capable of decomposing it. The direction of the current is always determined by the difference of affinity of the two conductors for the electro-negative element of the liquid. Negative electricity always proceeds from the metal, which by its greater affinity appropriates the electro-negative element, through the connecting wire to the other metal,-or, what comes to the same thingpositive electricity goes from the latter metal to that which is in the act of combination, and possibly, from this through the liquid to the inactive metal. The quantity of the electric current is directly proportional to the strength of the electro-chemical action. The greater the quantity of the electro-negative element taken up by the metal, the greater also will be the quantity of electricity which passes over,-provided always that no purely chemical action take place at the same time,-for the effect of this would be to weaken or arrest the electric current. The following circumstances accelerate the combination of the metal with the electronegative element of the liquid, and may therefore increase the electric current: Increase of affinity and diminution of cohesion in the metal,rise of temperature,-increased facility of conveying the negative electricity from the electro-negative metal to the liquid, depending upon cleanliness and extent of surface. The tension or intensity of the electric current is perhaps greater in proportion to the difference between the affinities of the two metals for the electro-negative element; the influence of the circumstances noticed in i, 1, must however be taken into account.

o. The metal endowed with the greater affinity for the electro-negative element of the liquid may, by its action, become covered with a product which may interrupt wholly or partially the contact between the liquid and the metal; in such a case, the affinity of the other metal may come into play, and give rise to a reversal of the current.

p. Two perfect conductors may produce a current, even without abstracting any element of the liquid, provided one of them give up one of its own elements to the liquid or the metal. Thus, from peroxide of manganese, lead, or silver, immersed in different liquids, positive electricity passes over through the galvanometer to platinum or copper. For, when a body of this nature gives up oxygen to the liquid, or transmits it by displacement of particles to the metal, the oxide, being more or less reduced, recovers its lost negative electricity by appropriating that which flows to it through the connecting wire from the platinum or the copper,the metal either receiving this negative electricity from the liquid which gives it up on combining with the oxygen, or evolving it directly, when it takes up the oxygen itself.]

Experiments with Water. On placing one above the other, brass, zinc, dry wood, damp wood, zinc, and brass, the last-mentioned brass imparted negative electricity to the condenser of the electrometer. (De la Rive.)

The same result was obtained with copper, zinc, four sheets of dry paper, one sheet of damp paper, zinc, copper;-the two copper-plates may also be omitted; the first zinc gave positive, the second negative electricity to the electrometer. Again, when a bar of zinc is wrapped round with paper and one-half of the paper wetted, the wet end imparts positive electricity to the electrometer; the dry end-if a damp sheet of paper be laid on the condenser to facilitate the conduction-negative electricity. (Fechner.) [Negative electricity accumulates in the last zinc (p. 342, c), positive electricity in the damp wood or paper; and these are communicated to the electrometer, when it is brought in contact with the zinc or the moisture.]

A solution of 1 part of potassium in 100 parts of mercury is, when placed in water, strongly positive towards platinum; polished lead is also positive towards platinum. Potassium being soluble in water, and oxide of lead likewise soluble though in a slighter degree, these substances can produce a strong current without the intervention of an acid. (Faraday*.)

If a strip of zinc and a strip of platinum in water deprived of air give at the commencement of the action a deflection of 15°, this deflection will be reduced to 1°, when the circuit has been closed for some time; but will again rise to 15°, after the circuit has been left open for 24 hours. Zine which has become inactive by immersion, together with platinum, in water free from air, is negative towards zinc freshly immersed. water containing air, on the contrary, a pair of zinc and copper gives a constant deflection of 15°. (Buff.)

In

Iron, which rusts when placed by itself under water, remains bright when in contact with zine, the latter alone becoming oxidated. (Wetzlar.) -The so-called Galvanized Iron is iron protected by a coating of pulverized zinc.

Polished lead is positive towards iron in pure water, tarnished lead negative. (Yorke.)-In pure water, lead is constantly, but very feebly, positive towards iron,-the iron likewise oxidating, though in a less degree. In spring-water, the lead is positive at first; but the iron soon becomes positive, remains so, and oxidates. (Wetzlar.) [Perhaps a deposit forms on the surface of the lead (p. 345, 0).]

Gold and platinum together produce no current in pure water (Walcker, Becquerel); neither does gold or platinum produce a current with magnetic iron ore, specular iron, red oxide of copper, or iron pyrites (Becquerel.)

If the wet and dry ends of a piece of peroxide of manganese be connected with the galvanometer, positive electricity passes from the dry end through the galvanometer to the wet end. A crystal of peroxide of manganese is feebly positive towards platinum in water, as shown by the galvanometer; the current soon ceases, but reappears if the circuit be left open for not less than five minutes. Platinum exhibits similar relations with graphite or anthracite, excepting that the latter becomes positive.

*These and most of the following experiments were so arranged that the metals in contact with the liquid were connected with the ends of the galvanometer. When it is said, in accordance with the received phraseology, that one metal is positive with regard to another, and the latter negative with regard to the former, it is to be understood that positive electricity goes from the negative metal through the galvanometer to the positive metal (and, as is sometimes assumed, from the positive metal through the liquid to the negative metal). In short, the positive metal is that which is chemically active-and, by taking up the electro-negative element of the liquid, developes negative electricity within itself, and sends it through the galvanometer to the inactive, negative metal,-or receives positive electricity from the latter (p. 342, c).

Likewise gold, magnetic iron ore, specular iron, red oxide of copper, and iron pyrites, become positive in water with peroxide of manganese or graphite. (Becquerel.) [With respect to peroxide of manganese, vid. p. 345, p.-Does the action of graphite result from its having absorbed oxygen from the air?] Platinum is positive towards peroxide of lead in pure water. (Schönbein.)

If platinum be laid on the condenser of the electrometer, damp paper on the platinum, peroxide of manganese on the paper, and the oxide of manganese touched with dry wood, the condenser will show positive electricity. When platinum and peroxide of manganese are connected with the galvanometer, positive electricity passes from the peroxide of manganese through the galvanometer to the platinum. In pure water, the current is very weak, but stronger with irregularly crystallized peroxide of manganese than with large single crystals, because the former is more prone to decomposition. If the oxide of manganese be left for a considerable time in water by itself, and then connected with platinum in nitric acid, the current at first goes the contrary way-a proof that the oxide of manganese has been superficially altered by the water. (Dela Rive.)

If zinc with copper and water give an indication of 4° in the voltaic electrometer, it will give 4 with silver, 4 with charcoal, 5 with gold, 5 with black sulphuret of mercury, 6 with iron pyrites, 6 with peroxide of manganese, and 9 with peroxide of lead. (Rosenchöld.)

Electrical series of metals in water, beginning with the most highly electro-positive: Zinc, lead, tin, iron, antimony, bismuth, copper, silver, gold. (Fechner.)

Experiments with Dilute Acids, not including Nitric Acid.-A solution of 1 part of potassium in 1000 parts of mercury is highly positive towards zinc.-Amalgam of zinc is positive towards zinc, and amalgam of tin towards tin. (H. Davy.)

Perfectly pure zinc dissolves more slowly in dilute sulphuric acid than commercial zinc, which contains 1 per cent. of iron, together with cadmium and traces of lead and tin-or than an alloy of 10 parts of zinc with 1 part of tin, lead, iron, or copper,-because these impurities give rise to local electro-chemical action (p. 344, i. 4). When commercial zinc and pure zinc are placed in dilute sulphuric acid of various degrees of strength (the annexed per centages show the quantities of anhydrous sulphuric acid in the liquid), the times required to furnish a given quantity of hydrogen gas are found to be as follows:

Hence, commercial zine is most quickly dissolved by dilute sulphuric acid containing from 25 to 43 per cent. of real acid, and pure zinc by that which contains from 30 to 43 per cent. The evolution of gas is very slow at first, but gradually increases, reaching its maximum in 10 minutes with commercial zinc, and after several hours with pure zine: with acid of 64 per cent, however, the evolution of gas soon diminishes. [Does this arise from the formation of a film of sulphate of zinc?] De la Rive.

Alloys of 10 parts of zinc, with 1 part of tin, lead, iron, or copper, being immersed in dilute sulphuric acid of various degrees of strength, a comparison of the times required for the evolution of a given quantity of hydrogen gas, with the corresponding intervals in the case of pure and commercial zinc, gives the following results:

With copper-zinc the evolution of gas continually diminishes, because the alloy becomes covered with a black film of oxide of copper [metallic copper?]; when this is removed, the evolution of gas again becomes rapid. -The solution of pure zinc is greatly accelerated by binding it round with platinum wire. (De la Rive.)

When four balls of zinc of equal size are immersed for an hour in equal quantities of dilute sulphuric acid, contained in four vessels of equal size, but different materials, the quantity of zinc dissolved in the glass vessel is found to be 15, in the silver vessel 51, in the gold vessel 65, and in the platinum vessel 79 millegrammes. On being afterwards immersed for an hour in four glass vessels containing equal quantities of acid of the same strength, the ball previously immersed in the other glass vessel loses 1.5, that from the silver vessel 5, from the gold 8, and from the platinum 11 millegrammes. (Bouchardat, Ann. Chim. Phys. 53, 284.) [Had the balls the same temperature in the second experiment?]

Balls of zinc immersed for the same time in dilute sulphuric acid, dilute hydrochloric acid, or solution of ammonia, lose, according to Bouchardat, the following quantities, varying with the nature of the containing vessel.

With balls of commercial zinc, the loss of weight in dilute sulphuric acid in a quarter of an hour amounts, in glass vessels to 9, in sulphur to 10, in lead to 310, in antimony to 350, in bismuth to 342, in silver to 665, and in platinum to 712. (Bouchardat.)

Two zinc plates of equal size being placed in dilute sulphuric acid (1 part oil of vitriol with from 8 to 16 of water), and one of them connected with a plate of polished lead, the second loses much less weight than the first (this is contrary to Bouchardat's statement); with hydrochloric acid an opposite result is obtained. (Runge, Pogg. 43, 581.)

To obtain amalgamated zinc, mercury is placed upon the zinc, together with dilute sulphuric acid, and both liquids spread upon the plate by means of a pad of cloth or linen, the acid being from time to time renewed. (Masson, Ann. Chim. Phys. 60, 334.) Or the bottom of a capacious dish being covered with mercury and sulphuric acid poured upon it, the zinc plate is immersed in the acid, its surface touching the mercury,-turned after two or three hours, and afterwards taken out. (Liebig, Ann. Pharm. 29, 111.) [This covering of the zinc with mercury depends on a peculiar galvanic action. The mercury,-which is in contact with the zinc at one point, and takes up the negative electricity set free in the zinc,-instead of giving rise to a transposition of atoms in the water, attaches itself, in consequence of its mobility, to the zinc, and thus imparts negative elec

tricity directly to the hydrogen-atom of the atom of water which has given up its oxygen to the zinc.]

Amalgamated zinc when alone is not attached by dilute sulphuric acid; but when it is connected with platinum or other metals, a powerful action takes place, the hydrogen gas being wholly evolved on the surface of the platinum, not upon the zinc. (Faraday.)-Amalgamated zinc immersed in dilute sulphuric ac 1 becomes covered after a time with gasbubbles, which adhere strongly to it; no loss of weight can be detected in the zinc, even after four-and-twenty hours. The adhering hydrogen gas appears then to protect the zinc from the action of the liquid. When amalgamated zinc is connected with platinum, the hydrogen being all transferred to the platinum, the zinc is dissolved. If the dilute sulphuric acid contains a little nitric acid mixed with it, that acid converts the hydrogen into ammonia, aud then the amalgamated zinc dissolves, even though not connected with platinum. (Daniell, De la Rive.) [But pure zinc likewise becomes covered with bubbles, and dissolves nevertheless.]-The coating of mercury makes the surface of the zinc uniform, so that the alloys possibly contained in it cannot give rise to any local electro-chemical action; it therefore makes commercial zinc like pure zinc. (Grove.) [But pure zinc dissolves, although the action goes on slowly,-amalgamated zinc not at all.] The mercury appears to prevent, in some unknown manner, the direct transference of negative electricity from the zinc to the hydrogen (p. 345, i, 5.)

Amalgamated zinc in dilute sulphuric acid is positive towards the same metal unamalgamated (H. Davy); because the latter, in consequence of the strong purely chemical action, is more quickly surrounded with saturated sulphuric acid [which, however, should be soonest removed by the rapid disengagement of gas]. (Faraday.)

When two pieces of amalgamated zinc of the same size are immersed in dilute sulphuric acid, and one of them is connected with copper, the latter piece loses 32:31 parts for every 1 part of hydrogen evolved at the surface of the copper (1 at. H. to 1 at. Zn.), while the other piece suffers no diminution. (Faraday.)

Amalgamated zinc produces with copper a much more copious current than ordinary zinc. (Poggendorff.)

An amalgamated zinc plate, connected with copper, and immersed in dilute sulphuric acid, loses more weight in the second half hour than in the first, in the third more than in the second, and so on, till it is again amalgamated. (Binks.)

Amalgamated zinc in dilute sulphuric acid, in connection with amalgamated copper which dips into mercury, or only with amalgamated platinum, is at first strongly positive, but the current ceases in a few minutes: but on replacing the amalgamated zinc by unamalgamated platinum, a current in the contrary direction is set up. The amalgamated metal is positive. The merenry probably combines with hydrogen, and thereby becomes as strongly positive as the amalgamated zinc. (Grove.)

Black lead or freshly ignited gas-coke placed in sulphuric acid with amalgamated zinc immediately liberates hydrogen gas; porous coke and box-wood charcoal, on the contrary, not till after some time, because they absorb the first portions of liberated hydrogen. If they are then placed by themselves in a solution of lead, copper, mercury, silver, or gold, they become covered with a thin metallic film, just as they liberate iodine from iodic acid. Coke retains hydrogen for forty-eight hours. (Smee.)

Zinc gives with iron in dilute sulphuric acid a current four times as